HomeMy WebLinkAboutPATEROS CREEK - PDP - PDP130011 - REPORTS - DRAINAGE REPORTMay 15, 2013
PRELIMINARY DRAINAGE AND
EROSION CONTROL REPORT
PATEROS CREEK
Fort Collins, Colorado
Prepared for:
Bucking Horse, LLC
3702 Manhattan Ave., Suite 201
Fort Collins, CO 80526
Prepared by:
200 South College Avenue, Suite 10
Fort Collins, Colorado 80524
Phone: 970.221.4158 Fax: 970.221.4159
www.northernengineering.com
Project Number: 687-001
This Drainage Report is consciously provided as a PDF.
Please consider the environment before printing this document in its entirety.
When a hard copy is absolutely necessary, we recommend double-sided printing.
May 15, 2013
City of Fort Collins
Stormwater Utility
700 Wood Street
Fort Collins, Colorado 80521
RE: Preliminary Drainage and Erosion Control Report for
PATEROS CREEK
Dear Staff:
Northern Engineering is pleased to submit this Preliminary Drainage and Erosion Control Report
for your review. This report accompanies the Project Development Plan submittal for the
proposed Pateros Creek development.
This report has been prepared in accordance to Fort Collins Stormwater Criteria Manual (FCSCM),
and serves to document the stormwater impacts associated with the proposed project. We
understand that review by the City is to assure general compliance with standardized criteria
contained in the FCSCM.
If you should have any questions as you review this report, please feel free to contact us.
Sincerely,
NORTHERN ENGINEERING SERVICES, INC.
Aaron Cvar, PE
Project Engineer
Pateros Creek
Preliminary Drainage Report
TABLE OF CONTENTS
I. GENERAL LOCATION AND DESCRIPTION .................................................................... 1
A. Location ............................................................................................................................................. 1
B. Description of Property ..................................................................................................................... 2
C. Floodplain ......................................................................................................................................... 3
II. DRAINAGE BASINS AND SUB-BASINS ........................................................................ 5
A. Major Basin Description .................................................................................................................... 5
III. DRAINAGE DESIGN CRITERIA .................................................................................... 5
A. Regulations ........................................................................................................................................ 5
B. Four Step Process .............................................................................................................................. 5
C. Development Criteria Reference and Constraints ............................................................................ 6
D. Hydrological Criteria ......................................................................................................................... 6
E. Hydraulic Criteria .............................................................................................................................. 6
F. Floodplain Regulations Compliance .................................................................................................. 7
G. Modifications of Criteria ................................................................................................................... 7
IV. DRAINAGE FACILITY DESIGN ..................................................................................... 7
A. General Concept ............................................................................................................................... 7
B. Specific Details .................................................................................................................................. 8
V. CONCLUSIONS .......................................................................................................... 9
A. Compliance with Standards .............................................................................................................. 9
B. Drainage Concept .............................................................................................................................. 9
References ......................................................................................................................... 10
APPENDICES:
APPENDIX A – Hydrologic Computations
APPENDIX B – Hydraulic Computations
B.1 – Storm Sewers (reserved for future use)
B.2 – Inlets (reserved for future use)
APPENDIX C – Detention and Water Quality Design Computations
APPENDIX D – Erosion Control Report
APPENDIX E – Supplemental Information: FEMA FIRMette, LOMR-F
Pateros Creek
Preliminary Drainage Report
LIST OF TABLES AND FIGURES:
Figure 1 – Aerial Photograph .................................................................................................. 2
Figure 2– Proposed Site Plan .................................................................................................. 3
Figure 3 – Existing Floodplains ............................................................................................... 4
Table 1 – Water Quality Pond Summary .................................................................................. 9
MAP POCKET:
Historic Drainage Exhibit
Offsite Basin Exhibit
Proposed Drainage Exhibit
Floodplain Exhibit
Pateros Creek
Preliminary Drainage Report 1
I. GENERAL LOCATION AND DESCRIPTION
A. Location
1. Vicinity Map
2. The project site is located in the southwest quarter of Section 2, Township 7 North,
Range 69 West of the 6th Principal Meridian, City of Fort Collins, County of Larimer,
State of Colorado.
3. The project site is located on the south side of Wood Street, and just north City of Fort
Collins Utilities Building. The Cache La Poudre River runs just to the north of the
project site.
4. The project site lies within Old Town Master Basin (City of Fort Collins, July 2003).
The site will outfall to the Cache La Poudre River. Due to the project site proximity to
the river, no detention is required for onsite runoff.
5. Residential development exists to the south and west of the site.
6. Offsite flows from the south are routed through the site via an existing CMP pipe at
the southeast corner of the site. This pipe drains runoff and excess water from the
existing pond located along the southern boundary of the site, as seen in Figure 1.
The pipe passes flows into the existing onsite pond. The existing onsite pond drains
via an existing 24-inch pipe into a swale, which conveys flows northeast to the Cache
La Poudre River. Please see the Offsite Basin Exhibit provided in the back map
pocket of this report.
Pateros Creek
Preliminary Drainage Report 2
B. Description of Property
1. The development area is roughly 9.3 net acres.
Figure 1 – Aerial Photograph
2. The subject property now consists of vacant ground. In 2012 the site was cleared of
a mobile home park that had existed for several decades on the property. The ground
cover generally consists of native seeding. Existing ground slopes are mild (i.e., 1 -
3±%) through the interior of the property. General topography slopes from southwest
to the northeast towards the Cache La Poudre River.
3. According to the United States Department of Agriculture (USDA) Natural Resources
Conservation Service (NRCS) Soil Survey website:
http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx,
the site consists of Paoli fine sandy loam and Table Mountain Loam, which fall into
Hydrologic Soil Group B; and Table Mountain Loam. More site-specific exploration
found varying materials including sandy clay with occasional sand layers and sandy
gravel. See the Geotechnical Engineering Report by Earth Engineering Consultants,
Inc. for additional information.
4. The proposed project will create a residential development. Associated roadways,
water and sewer lines will be constructed with the development. A water quality
forebay will be constructed near the southeast corner of the site. The existing wet
pond at the southeast corner of the site will be utilized for stacked detention.
Pateros Creek
Preliminary Drainage Report 3
Figure 2– Proposed Site Plan
5. There are no irrigation ditches or related facilities in the vicinity of the project site.
6. The proposed land use is residential.
C. Floodplain
1. A portion of the subject property is encroached by the FEMA 100-year floodplain
(Cache La Poudre River). Please see the Floodplain Exhibit provided in the back map
pocket of this report.
Pateros Creek
Preliminary Drainage Report 4
Figure 3 – Existing Floodplains
2. No offsite improvements are proposed with the project.
3. FEMA FIRM Panel Number 977 for Larimer County, dated June 17, 2008 is
referenced in this study. A FIRMette of the area is provided in the appendix. A
LOMR-F was completed March 22, 2012 (FEMA case no. 12-08-0323A). A copy of
this LOMR-F is provided in the Appendix. All lots removed from the FEMA 100-year
flood zone are noted on the Floodplain Exhibit (please see back map pocket).
Regulatory Flood Protection Elevations and Base Flood Elevations are shown on this
exhibit. Additionally, requirements for the elevation of the lowest floor, HVAC and
electrical, the type of foundation for the LOMR-F lots, floodplain permit and CO
requirements, and no-rise certification requirements in the floodway are noted on the
Floodplain Exhibit.
4. Base (100-year) flood elevations range from roughly 4973 at the east end of the site
to 4977 at the west end of the site. These elevations are referenced to the City of
Fort Collins NGVD 29.
5. The proposed structures are located outside of the 100-year floodplain; however some
of the proposed residential structures lie within the 500-year floodplain. Two lots are
shown within the West Vine Floodway (Lots 1 and 2). It has been noted on the
Floodplain Exhibit (please see back map pocket) that these lots cannot be developed
until the West Vine Floodway is removed.
6. The Cache La Poudre half-foot floodway is located outside of the development area.
No fill is proposed within the floodway
7. Stabilization measures are currently being proposed along the bend in the Cache La
Poudre River northwest of the project site. All stabilization design work is being
conducted by the City of Fort Collins.
8. It is noted that the vertical datum utilized for site survey work is the City of Fort
Collins Benchmark #10-00 (Elevation=4988.43, Ft. Collins Unadjusted NGVD 29).
Pateros Creek
Preliminary Drainage Report 5
II. DRAINAGE BASINS AND SUB-BASINS
A. Major Basin Description
1. The project The project site lies within Old Town Master Basin (City of Fort Collins,
July 2003). The site will outfall to the Cache La Poudre River. Due to the project
site proximity to the river, no detention is required for onsite runoff.
B. Sub-Basin Description
2. The subject property historically drains overland towards the Cache La Poudre River,
which runs north of the site. A more detailed description of the project drainage
patterns follows in Section IV.A.4., below.
3. Flows from the pond just to the south of the site historically drain through the project
site. A 12-inch diameter pipe conveys flow from the offsite pond into the existing wet
pond at the southeast corner of the site. A 24-inch pipe drains the existing wet pond
into an offsite swale that runs northeast into the Cache La Poudre River. No
modifications are proposed to the 24-inch outlet pipe. Therefore, flows will continue
to pass through the existing onsite wet pond with the proposed development.
III. DRAINAGE DESIGN CRITERIA
A. Regulations
There are no optional provisions outside of the FCSCM proposed with the proposed
project.
B. Four Step Process
The overall stormwater management strategy employed with the proposed project utilizes
the “Four Step Process” to minimize adverse impacts of urbanization on receiving waters.
The following is a description of how the proposed development has incorporated each
step.
Step 1 – Employ Runoff Reduction Practices
Several techniques have been utilized with the proposed development to facilitate the
reduction of runoff peaks, volumes, and pollutant loads as the site is developed from the
current use by implementing multiple Low Impact Development (LID) strategies including:
Conserving existing amenities in the site including the existing vegetated areas.
Providing vegetated open areas throughout the site to reduce the overall impervious
area and to minimize directly connected impervious areas (MDCIA).
Routing flows, to the extent feasible, through vegetated swales to increase time of
concentration, promote infiltration and provide initial water quality.
Step 2 – Implement BMPs That Provide a Water Quality Capture Volume (WQCV) with
Slow Release
The efforts taken in Step 1 will facilitate the reduction of runoff; however, urban
development of this intensity will still generate stormwater runoff that will require
additional BMPs and water quality. The majority of stormwater runoff from the site will
ultimately be routed to the southeast corner of the site, where it will be intercepted and
treated in the main water quality forebay prior to entering the existing wet pond and then
exiting the site.
Pateros Creek
Preliminary Drainage Report 6
Step 3 – Stabilize Drainageways
There are no major drainageways within the subject property. While this step may not
seem applicable to proposed development, the project indirectly helps achieve stabilized
drainageways nonetheless. By providing water quality where none previously existed,
sediment with erosion potential is removed from the downstream drainageway systems
and Cache La Poudre River. Furthermore, this project will pay one-time stormwater
development fees, as well as ongoing monthly stormwater utility fees, both of which help
achieve City-wide drainageway stability.
Step 4 – Implement Site Specific and Other Source Control BMPs.
The proposed project will improve upon site specific source controls compared to historic
conditions:
Trash, waste products, etc. that were previously left exposed with the historic trailer
park will no longer be allowed to exposure to runoff and transport to the adjacent
Cache La Poudre River. The proposed development will eliminate these sources of
potential pollution.
C. Development Criteria Reference and Constraints
The subject property is surrounded by currently developed properties. Thus, several
constraints have been identified during the course of this analysis that will impact the
proposed drainage system including:
Existing elevations along the west and south property lines will be maintained.
As previously mentioned, overall drainage patterns of the existing site will be
maintained.
Elevations of existing downstream facilities that the subject property will release to
will be maintained.
D. Hydrological Criteria
1. The City of Fort Collins Rainfall Intensity-Duration-Frequency Curves, as depicted in
Figure RA-16 of the FCSCM, serve as the source for all hydrologic computations
associated with the proposed development. Tabulated data contained in Table RA-7
has been utilized for Rational Method runoff calculations.
2. The Rational Method has been employed to compute stormwater runoff utilizing
coefficients contained in Tables RO-11 and RO-12 of the FCSCM.
3. Three separate design storms have been utilized to address distinct drainage
scenarios. A fourth design storm has also been computed for comparison purposes.
The first design storm considered is the 80th percentile rain event, which has been
employed to design the project’s water quality features. The second event analyzed is
the “Minor,” or “Initial” Storm, which has a 2-year recurrence interval. The third
event considered is the “Major Storm,” which has a 100-year recurrence interval.
The fourth storm computed, for comparison purposes only, is the 10-year event.
4. No other assumptions or calculation methods have been used with this development
that are not referenced by current City of Fort Collins criteria.
E. Hydraulic Criteria
1. As previously noted, the subject property maintains historic drainage patterns.
Pateros Creek
Preliminary Drainage Report 7
2. All drainage facilities proposed with the project are designed in accordance with
criteria outlined in the FCSCM and/or the Urban Drainage and Flood Control District
(UDFCD) Urban Storm Drainage Criteria Manual.
3. As stated above, portions of the subject property is located in a FEMA regulatory
floodplain.
4. The proposed project does not propose to modify any natural drainageways.
F. Floodplain Regulations Compliance
1. As previously mentioned, all structures are located outside of the Cache La Poudre
100-year floodplain, and thus the structures are not subject to any floodplain
regulations. However, extra care has been taken to ensure that neither existing nor
proposed structures will suffer damage during the 100-year storm as a result of the
proposed development.
2. Stabilization measures are currently being proposed along the bend in the Cache La
Poudre River northwest of the project site. All stabilization design work is being
conducted by the City of Fort Collins.
3. Critical facilities are prohibited within the 100-year and 500-year flood fringe.
4. A floodplain use permit must be obtained prior to any work to be done within the
floodplain prior to construction. A no-rise certification must be completed for any
work to be done within the floodway prior to construction.
5. No floatable items are proposed within the floodway. Any floatable items within the
floodway must be anchored to prevent flotation.
G. Modifications of Criteria
1. The proposed development is not requesting any modifications to criteria at this time.
IV. DRAINAGE FACILITY DESIGN
A. General Concept
1. The main objectives of the project drainage design are to maintain existing drainage
patterns, and to ensure no adverse impacts to any adjacent properties.
2. The existing pond to the south of the site historically drains through the project site.
Off-site drainage flows and patterns will be maintained and accounted for with the
proposed development.
3. A list of tables and figures used within this report can be found in the Table of
Contents at the front of the document. The tables and figures are located within the
sections to which the content best applies.
4. The drainage patterns anticipated for proposed drainage basins are described below.
Basin 1
Basin 1 consists of backs of proposed residential lots. This basin will be allowed to
sheet flow across a large natural vegetated buffer prior to entry into the Cache La
Poudre River, just to the north of this basin. Due to reduction in area draining directly
to the Cache La Poudre River, Historic 2-, 10-, and 100-year flows will be reduced.
Pateros Creek
Preliminary Drainage Report 8
2-yr Flow 10-yr Flow 100-yr Flow
(cfs) (cfs) (cfs)
Historic Cond. 1.01 1.72 4.53
Proposed Cond. 0.42 0.72 1.86
Soil samples have been taken which indicate that runoff from Basin 1 will infiltrate
significantly prior reaching the Cache La Poudre River. We will provide further
analysis and documentation at Final Design.
Basin 2
Basin 2 consists of residential lots and proposed street/sidewalk. This basin will drain
via street curb and gutter to a proposed storm sewer system and into the proposed
water quality forebay to be located just west (upstream) of the existing wet pond.
Basin 3
Basin 3 consists of residential lots and proposed street/sidewalk. This basin will drain
via street curb and gutter to a proposed storm sewer system and into the proposed
water quality forebay to be located just west (upstream) of the existing wet pond.
Basin 4
Basin 4 consists of backs of residential lots and an open area behind lots. This basin
will drain via swale and then via street curb and gutter to a proposed storm sewer
system and into the proposed water quality forebay to be located just west (upstream)
of the existing wet pond.
Basin 5
Basin 5 consists of residential lots and proposed street/sidewalk. This basin will drain
via street curb and gutter to a proposed storm sewer system and into the proposed
water quality forebay to be located just west (upstream) of the existing wet pond.
Basin 6
Basin 6 consists of residential lots and proposed street/sidewalk. This basin will drain
via street curb and gutter to a proposed storm sewer system and into the proposed
water quality forebay to be located just west (upstream) of the existing wet pond.
Basin 7
Basin 7 consists of backs of residential lots. This basin will be allowed to sheet flow
across a large natural vegetated buffer area. The length of this area is sufficient that
we believe all storm runoff will infiltrate or be captured in localized depressions prior
to entry into the Cache La Poudre River.
A full-size copy of the Drainage Exhibit can be found in the Map Pocket at the end of
this report.
B. Specific Details
1. Water quality treatment is being provided for the proposed development in the form of
a water quality forebay as previously described. Further documentation of treatment
volumes and removal rates of stormwater BMPs will be documented with the Final
Drainage Report prepared during the City FCP process. LID features will be
incorporated in the design of the water quality forebay at Final design. We anticipate
Pateros Creek
Preliminary Drainage Report 9
a PLD type bottom to be incorporated in part of the forebay.
Final design details, construction documentation, and Standard Operating
Procedures (SOP) Manual shall be provided to the City of Fort Collins for
review prior to Final Development Plan approval. A final copy of the approved
SOP manual shall be provided to City and must be maintained on-site by the
entity responsible for the facility maintenance. Annual reports must also be
prepared and submitted to the City discussing the results of the maintenance
program (i.e. inspection dates, inspection frequency, volume loss due to
sedimentation, corrective actions taken, etc.).
2. Table 1, below, summarizes the water quality information for the proposed water
quality pond.
Table 1 – Water Quality Pond Summary
Water Quality Water Quality Pond Spillway Top of Pond
Capture Volume WSEL Elevation Elevation
(AC-FT) (FT) (FT) (FT)
0.110 4971 +/- (prelim.) 4971.5 +/- (prelim.) 4972 +/- (prelim.)
3. Proper maintenance of the drainage facilities designed with the proposed
development is a critical component of their ongoing performance and effectiveness.
The water quality pond may be easily accessed by maintenance staff via the gentle
slope provided to the bottom of the pond from the south side.
4. The drainage features associated with the proposed project are all private facilities,
located on private property.
5. The proposed outfall for the majority of the site is the existing wet pond at the
southeast corner of the site. This wet pond has drains via an existing 24-inch pipe
into a swale, which conveys flows northeast to the Cache La Poudre River. Stacked
detention (detention over the permanent water surface elevation) within the existing
wet pond is proposed in order to maintain capacity within the receiving offsite swale.
Preliminary calculations provided in the appendix show a detention volume of 0.94
acre-feet with a peak 100-year release rate of 1.30 cfs.
V. CONCLUSIONS
A. Compliance with Standards
1. The drainage design proposed with the proposed project complies with the City of Fort
Collins’ Stormwater Criteria Manual.
2. The drainage design proposed with this project complies with the Old Town Master
Basin (City of Fort Collins, July 2003).
3. The drainage plan and stormwater management measures proposed with the
proposed development are compliant with all applicable State and Federal regulations
governing stormwater discharge.
4. The proposed development is in compliance with Chapter 10 of City Code.
B. Drainage Concept
1. The drainage design proposed with this project will effectively limit any potential
Pateros Creek
Preliminary Drainage Report 10
damage associated with its stormwater runoff by providing detention and a water
quality forebay.
2. The drainage concept for the proposed development is consistent with the Old Town
Master Basin (City of Fort Collins, July 2003).
References
1. City of Fort Collins Landscape Design Guidelines for Stormwater and Detention Facilities,
November 5, 2009, BHA Design, Inc. with City of Fort Collins Utility Services.
2. Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, as adopted by Ordinance No.
174, 2011, and referenced in Section 26-500 (c) of the City of Fort Collins Municipal Code.
3. Larimer County Urban Area Street Standards, Adopted January 2, 2001, Repealed and
Reenacted, Effective October 1, 2002, Repealed and Reenacted, Effective April 1, 2007.
4. Soils Resource Report for Larimer County Area, Colorado, Natural Resources Conservation
Service, United States Department of Agriculture.
5. Urban Storm Drainage Criteria Manual, Volumes 1-3, Urban Drainage and Flood Control
District, Wright-McLaughlin Engineers, Denver, Colorado, Revised April 2008.
6. Preliminary Subsurface Exploration Report, 912 Wood Street, November 17, 2011, Earth
Engineering Consultants, Inc.
APPENDIX A
HYDROLOGIC COMPUTATIONS
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: 687-001
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: ATC
Asphalt ……....……………...……….....…...……………….……………………………… 0.95 100% Date:
Concrete …….......……………….….……….………………..….…………………………… 0.95 90%
Gravel ……….…………………….….…………………………..…………………………… 0.50 40%
Roofs …….…….………………..……………….……………………………………………. 0.95 90%
Pavers…………………………...………………..…………………………………………… 0.40 22%
Lawns and Landscaping
Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0%
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year Cf
= 1.00 100-year Cf = 1.25
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
H1 203425 4.67 0.000 0.000 0.436 0.776 3.458 0.17 0.17 0.21 15%
H2 201247 4.62 0.000 0.000 0.415 0.000 4.205 0.09 0.09 0.11 8%
HISTORIC COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.
10-year Cf = 1.00
March 12, 2013
Overland Flow, Time of Concentration:
Project: 687-001
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt = L / 60V
Tc = Ti + Tt (Equation RO-2)
Velocity (Gutter Flow), V = 20·S½
Velocity (Swale Flow), V = 15·S½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Is Length
>500' ?
C*Cf
(2-yr
Cf=1.00)
C*Cf
(10-yr
Cf=1.00)
C*Cf
(100-yr
Cf=1.25)
Length,
L
(ft)
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
2-yr
Tc
Rational Method Equation: Project: 687-001
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
1H14.6732 32 30 0.17 0.17 0.21 1.26 2.14 4.52 1.0 1.7 4.5
2H24.6245 45 44 0.09 0.09 0.11 0.99 1.69 3.51 0.4 0.7 1.7
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
HISTORIC RUNOFF COMPUTATIONS
C100
Design
Point
Flow,
Q100
(cfs)
Flow,
Q2
(cfs)
10-yr
Tc
(min)
2-yr
Tc
(min)
C2
Flow,
Q10
(cfs)
Intensity,
i100
(in/hr)
Basin(s)
ATC
March 12, 2013
Intensity,
i10
(in/hr)
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
C10
Q C f C i A
CHARACTER OF SURFACE:
Runoff
Coefficient
Percentage
Impervious Project: 687-001
Streets, Parking Lots, Roofs, Alleys, and Drives: Calculations By: ATC
Asphalt ……....……………...……….....…...……………….……………………………… 0.95 100% Date:
Concrete …….......……………….….……….………………..….…………………………… 0.95 90%
Gravel ……….…………………….….…………………………..…………………………… 0.50 40%
Roofs …….…….………………..……………….……………………………………………. 0.95 90%
Pavers…………………………...………………..…………………………………………… 0.40 22%
Lawns and Landscaping
Sandy Soil ……..……………..……………….…………………………………………….. 0.15 0%
Clayey Soil ….….………….…….…………..………………………………………………. 0.25 0% 2-year Cf
= 1.00 100-year Cf = 1.25
Basin ID
Basin Area
(s.f.)
Basin Area
(ac)
Area of
Asphalt
(ac)
Area of
Concrete
(ac)
Area of
Roofs
(ac)
Area of
Gravel
(ac)
Area of
Lawns and
Landscaping
(ac)
2-year
Composite
Runoff
Coefficient
10-year
Composite
Runoff
Coefficient
100-year
Composite
Runoff
Coefficient
Composite
% Imperv.
1 51826 1.19 0.000 0.028 0.184 0.000 0.979 0.17 0.17 0.21 16%
2 68364 1.57 0.360 0.110 0.275 0.000 0.824 0.45 0.45 0.56 45%
3 41042 0.94 0.295 0.083 0.207 0.000 0.358 0.59 0.59 0.74 59%
4 61286 1.41 0.000 0.059 0.390 0.000 0.958 0.30 0.30 0.38 29%
5 36917 0.85 0.260 0.083 0.207 0.000 0.298 0.62 0.62 0.77 61%
6 111161 2.55 0.300 0.126 0.459 0.000 1.667 0.33 0.33 0.41 32%
7 33891 0.78 0.000 0.014 0.092 0.000 0.672 0.13 0.13 0.16 12%
2 - 6 318770 7.32 1.215 0.460 1.538 0.000 4.104 0.42 0.42 0.52 41%
DEVELOPED COMPOSITE % IMPERVIOUSNESS AND RUNOFF COEFFICIENT CALCULATIONS
Runoff Coefficients are taken from the City of Fort Collins Storm Drainage Design Criteria and Construction Standards, Table 3-3. % Impervious taken from UDFCD USDCM, Volume I.
Overland Flow, Time of Concentration:
Project: 687-001
Calculations By:
Date:
Gutter/Swale Flow, Time of Concentration:
Tt = L / 60V
Tc = Ti + Tt (Equation RO-2)
Velocity (Gutter Flow), V = 20·S½
Velocity (Swale Flow), V = 15·S½
NOTE: C-value for overland flows over grassy surfaces; C = 0.25
Is Length
>500' ?
C*Cf
(2-yr
Cf=1.00)
C*Cf
(10-yr
Cf=1.00)
C*Cf
(100-yr
Cf=1.25)
Length,
L
(ft)
Slope,
S
(%)
Ti
2-yr
(min)
Ti
10-yr
(min)
Ti
100-yr
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
Length,
L
(ft)
Slope,
S
(%)
Velocity,
V
(ft/s)
Tt
(min)
2-yr
Tc
Rational Method Equation: Project: 687-001
Calculations By:
Date:
From Section 3.2.1 of the CFCSDDC
Rainfall Intensity:
1 1 1.19 12 12 11 0.17 0.17 0.21 2.09 3.57 7.42 0.4 0.7 1.9
2 2 1.57 18 18 17 0.45 0.45 0.56 1.73 2.95 6.20 1.2 2.1 5.5
3 3 0.94 14 14 13 0.59 0.59 0.74 1.92 3.29 6.92 1.1 1.8 4.8
4 4 1.41 19 19 17 0.30 0.30 0.38 1.68 2.86 6.10 0.7 1.2 3.3
5 5 0.85 13 13 12 0.62 0.62 0.77 1.98 3.39 7.29 1.0 1.8 4.8
6 6 2.55 22 22 21 0.33 0.33 0.41 1.53 2.61 5.46 1.3 2.2 5.7
7 7 0.78 15 15 15 0.13 0.13 0.16 1.87 3.19 6.62 0.2 0.3 0.8
Intensity,
i10
(in/hr)
Rainfall Intensity taken from the City of Fort Collins Storm Drainage Design Criteria (CFCSDDC), Figure 3.1
C10
Area, A
(acres)
Intensity,
i2
(in/hr)
100-yr
Tc
(min)
DEVELOPED RUNOFF COMPUTATIONS
C100
Design
Point
Flow,
Q100
(cfs)
Flow,
Q2
(cfs)
10-yr
Tc
(min)
2-yr
Tc
(min)
C2
Flow,
Q10
(cfs)
Intensity,
i100
(in/hr)
Basin(s)
ATC
March 12, 2013
Q C f C i A
APPENDIX B
HYDRAULIC COMPUTATIONS
B.1 – Storm Sewers (reserved for future use)
B.2 – Inlets (reserved for future use)
APPENDIX B.1
STORM SEWERS (reserved for future use)
APPENDIX B.2
INLETS (reserved for future use)
APPENDIX C
DETENTION AND WATER QUALITY DESIGN COMPUTATIONS
ATC
Pond No : Exist. Wet Pond
Overall
100-yr
0.52
Area (A)= 7.32 acres 41067 ft
3
Max Release Rate = 1.30 cfs 0.94 ac-ft
Time Time 100-yr
Intensity Q
100
Inflow
(Runoff)
Volume
Outflow
(Release)
Volume
Storage
Detention
Volume
(mins) (secs) (in/hr) (cfs) (ft
3
) (ft
3
) (ft
3
)
5 300 9.950 37.87 11362 390.0 10972.1
10 600 7.720 29.39 17631 780.0 16851.2
15 900 6.520 24.82 22336 1170.0 21166.0
20 1200 5.600 21.32 25579 1560.0 24019.0
25 1500 4.980 18.96 28434 1950.0 26483.8
30 1800 4.520 17.20 30969 2340.0 28628.9
35 2100 4.080 15.53 32613 2730.0 29883.2
40 2400 3.740 14.24 34166 3120.0 31046.2
45 2700 3.460 13.17 35559 3510.0 32049.4
50 3000 3.230 12.29 36884 3900.0 32984.0
55 3300 3.030 11.53 38060 4290.0 33770.2
60 3600 2.860 10.89 39191 4680.0 34510.7
65 3900 2.720 10.35 40378 5070.0 35308.3
70 4200 2.590 9.86 41406 5460.0 35946.0
75 4500 2.480 9.44 42479 5850.0 36629.4
80 4800 2.380 9.06 43484 6240.0 37244.3
85 5100 2.290 8.72 44455 6630.0 37824.9
90 5400 2.210 8.41 45426 7020.0 38405.6
95 5700 2.130 8.11 46214 7410.0 38803.5
100 6000 2.060 7.84 47047 7800.0 39247.1
105 6300 2.000 7.61 47961 8190.0 39770.6
110 6600 1.940 7.38 48737 8580.0 40157.1
115 6900 1.890 7.19 49639 8970.0 40669.3
120 7200 1.840 7.00 50427 9360.0 41067.2
Input Variables Results
Calculations By:
Design Point
Design Storm Required Detention Volume
Developed "C" =
DETENTION POND CALCULATION; FAA METHOD
Project Number : 687-001
Project Name : Pateros Creek
Project Location : Fort Collins
WATER QUALITY POND DESIGN CALCULATIONS
Water Quality Pond
Project: 687-001
By: ATC
Date: 3/12/13
REQUIRED STORAGE & OUTLET WORKS:
BASIN AREA = 7.320 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS PERCENT = 41.00 <-- INPUT from impervious calcs
BASIN IMPERVIOUSNESS RATIO = 0.4100 <-- CALCULATED
WQCV (watershed inches) = 0.182 <-- CALCULATED from Figure EDB-2
WQCV (ac-ft) = 0.111 <-- CALCULATED from UDFCD DCM V.3 Section 6.5
WQ Depth (ft) = ** <-- INPUT from stage-storage table
AREA REQUIRED PER ROW, a (in
2
) = ** <-- CALCULATED from Figure EDB-3
CIRCULAR PERFORATION SIZING:
dia (in) = ** <-- INPUT from Figure 5
n = ** <-- INPUT from Figure 5
t (in) = ** <-- INPUT from Figure 5
number of rows = ** <-- CALCULATED from WQ Depth and row spacing
**To be completed at final design
APPENDIX D
EROSION CONTROL REPORT
Pateros Creek
Preliminary Erosion Control Report
EROSION CONTROL REPORT
A comprehensive Erosion and Sediment Control Plan (along with associated details) will be included
with the final construction drawings. It should be noted, however, that any such Erosion and
Sediment Control Plan serves only as a general guide to the Contractor. Staging and/or phasing of
the BMPs depicted, and additional or different BMPs from those included may be necessary during
construction, or as required by the authorities having jurisdiction.
It shall be the responsibility of the Contractor to ensure erosion control measures are properly
maintained and followed. The Erosion and Sediment Control Plan is intended to be a living
document, constantly adapting to site conditions and needs. The Contractor shall update the
location of BMPs as they are installed, removed or modified in conjunction with construction
activities. It is imperative to appropriately reflect the current site conditions at all times.
The Erosion and Sediment Control Plan shall address both temporary measures to be implemented
during construction, as well as permanent erosion control protection. Best Management Practices
from the Volume 3, Chapter 7 – Construction BMPs will be utilized. Measures may include, but are
not limited to, silt fencing along the disturbed perimeter, gutter protection in the adjacent roadways
and inlet protection at existing and proposed storm inlets. Vehicle tracking control pads, spill
containment and clean-up procedures, designated concrete washout areas, dumpsters, and job site
restrooms shall also be provided by the Contractor.
Grading and Erosion Control Notes can be found on the Utility Plans. The Final Plans will contain a
full-size Erosion Control sheet as well as a separate sheet dedicated to Erosion Control Details. In
addition to this report and the referenced plan sheets, the Contractor shall be aware of, and adhere
to, the applicable requirements outlined in the Development Agreement for the development. Also,
the Site Contractor for this project will be required to secure a Stormwater Construction General
Permit from the Colorado Department of Public Health and Environment (CDPHE), Water Quality
Control Division – Stormwater Program, prior to any earth disturbance activities. Prior to securing
said permit, the Site Contractor shall develop a comprehensive StormWater Management Plan
(SWMP) pursuant to CDPHE requirements and guidelines. The SWMP will further describe and
document the ongoing activities, inspections, and maintenance of construction BMPs.
APPENDIX E
SUPPLEMENTAL INFORMATION: FEMA FIRMETTE, LOMR-F
Date: Case No.: 12-08-0323A LOMR-F
Federal Emergency Management Agency
Washington, D.C. 20472
Page 1 of 2 March 22, 2012
COMMUNITY AND MAP PANEL INFORMATION LEGAL PROPERTY DESCRIPTION
COMMUNITY
AFFECTED
MAP PANEL
NUMBER: 08069C0977G
DATE: 6/17/2008
FLOODING SOURCE: CACHE LA POUDRE RIVER
LARIMER COUNTY, COLORADO
(Unincorporated Areas)
A portion of Section 2, Township 7 North, Range 69 West, 6th P.M.,
as described in the Special Warranty Deed recorded as Reception
No. 20110057190, in the Office of the Recorder, Larimer County,
Colorado.
The portion of property is more particularly described by the following
COMMUNITY NO.: 080101 metes and bounds:
DATUM: NAD 83
APPROXIMATE LATITUDE & LONGITUDE OF PROPERTY: 40.600, -105.088
SOURCE OF LAT & LONG: GOOGLE EARTH PRO
DETERMINATION DOCUMENT (REMOVAL)
LETTER OF MAP REVISION BASED ON FILL
DETERMINATION
STREET FLOOD
ZONE
LOWEST
LOT
ELEVATION
(NAVD 88)
BLOCK/
SECTION
LOT SUBDIVISION
OUTCOME 1% ANNUAL
CHANCE
FLOOD
ELEVATION
(NAVD 88)
LOWEST
ADJACENT
GRADE
ELEVATION
(NAVD 88)
WHAT IS
REMOVED FROM
THE SFHA
-- 4976.9 to
4978.2 feet
4976.8 to --
4978.1 feet
X
(shaded)
Portion of
Property
-- -- 912 Wood Street
Special Flood Hazard Area (SFHA) - The SFHA is an area that would be inundated by the flood having a 1-percent chance of being
equaled or exceeded in any given year (base flood).
ADDITIONAL CONSIDERATIONS (Please refer to the appropriate section on Attachment 1 for the additional considerations listed below.)
LEGAL PROPERTY DESCRIPTION
Date: Case No.: 12-08-0323A LOMR-F
Federal Emergency Management Agency
Washington, D.C. 20472
Page 2 of 2 March 22, 2012
LETTER OF MAP REVISION BASED ON FILL
DETERMINATION DOCUMENT (REMOVAL)
ATTACHMENT 1 (ADDITIONAL CONSIDERATIONS)
LEGAL PROPERTY DESCRIPTION (CONTINUED)
COMMENCING at the southwest sixteenth corner of Section 2; thence N82º46'17"E, 742.17 feet to the POINT
OF BEGINNING; thence S72º29'58"E, 11.00 feet; thence S61º00'36"E, 56.26 feet; thence S45º51'29"E, 28.00
feet; thence S11º34'53"E, 12.83 feet; thence S33º46'31"E, 57.28 feet; thence S19º36'59"E, 10.57 feet; thence
S41º14'18"W, 13.40 feet; thence S53º25'50"W, 5.22 feet; thence S23º39'30"W, 3.62 feet; thence S06º29'07"E,
16.57 feet; thence S01º58'10"W, 5.67 feet; thence S31º19'01"E, 15.75 feet; thence S73º17'41"E, 25.80 feet;
thence S50º36'37"E, 4.30 feet; thence S18º08'58"E, 18.35 feet; thence S04º38'57"W, 8.51 feet; thence
S26º03'53"E, 74.26 feet; thence S12º18'35"E, 42.71 feet; thence S01º04'35"E, 20.34 feet; thence
S19º40'18"E, 54.06 feet; thence S34º19'30"E, 20.20 feet; thence S37º32'20"E, 22.09 feet; thence
S89º55'53"W, 194.56 feet; thence N21º43'47"W, 171.33 feet; thence N33º07'30"W, 110.80 feet; thence
N27º04'37"E, 191.50 feet to the POINT OF BEGINNING.
FILL RECOMMENDATION (This Additional Consideration applies to the preceding 1 Property.)
The minimum NFIP criteria for removal of the subject area based on fill have been met for this request and the
community in which the property is located has certified that the area and any subsequent structure(s) built on the
filled area are reasonably safe from flooding. FEMA’s Technical Bulletin 10-01 provides guidance for the
construction of buildings on land elevated above the base flood elevation through the placement of fill. A copy of
Technical Bulletin 10-01 can be obtained by calling the FEMA Map Assistance Center toll free at (877) 336-2627
(877-FEMA MAP) or from our web site at http://www.fema.gov/mit/tb1001.pdf. Although the minimum NFIP
standards no longer apply to this area, some communities may have floodplain management regulations that are
more restrictive and may continue to enforce some or all of their requirements in areas outside the Special Flood
Hazard Area.
PORTIONS OF THE PROPERTY REMAIN IN THE SFHA (This Additional Consideration applies to the
preceding 1 Property.)
Portions of this property, but not the subject of the Determination/Comment document, may remain in the Special
Flood Hazard Area. Therefore, any future construction or substantial improvement on the property remains
subject to Federal, State/Commonwealth, and local regulations for floodplain management.
This attachment provides additional information regarding this request. If you have any questions about this attachment, please contact the
FEMA Map Assistance Center toll free at (877) 336-2627 (877-FEMA MAP) or by letter addressed to the Federal Emergency Management
Agency, LOMC Clearinghouse, 7390 Coca Cola Drive, Ste 204, Hanover, MD 21076.
Luis Rodriguez, P.E., Chief
Engineering Management Branch
Federal Insurance and Mitigation Administration
River District Block One Mixed Use
Preliminary Erosion Control Report
MAP POCKET
DRAINAGE EXHIBITS
WOOD STREET
(ROW VARIES)
�����:
����� ������� �/������ �
802 ���� ��.
���� �������,
�� 80521
�����:
���� �� ���� �������
�� ��� 580
���� �������,
�� 80522
H1
4.67 ��
H2
4.62 ��
4980
4981
4982
4983
4984
4979
4978
4978
4975
4975
4976
4977
4975
4972
4975
4971
4972
4973
4974
4976
4971
4970
4969
4970
4971
4971
4970
4970
4971
4970
4971
4972
4971
4973
4971
4972
4968
4970
4969
4971
4972
4973
4974
4973
4973
4974
4975
4974
4975
4980
4976
4977
4978
4979
4980
4977
4978
4979
4981
4980
4976
4977
4978
4979
4980
4978
4979
4981
4982
4983
4985
4984
4970
4970
4969
4971
4972
4972
7.9'
6.1'
X X X X X X
X X
X X X
X X X
X X X
X X X
X X X
X
X X X
X X X
X
X
X X X X
X X X X X X X X
X
X
X
X
X X X
X
SS SS SS SS SS SS SS SS SS SS
SS
SS
SS SS
SS
SS
SS
SS
SS SS
SS SS
SS SS SS
SS SS
SS
SS SS
SS
SS
S
S
S
S
S
W
WV
W
W W
SS
E E
T T
T
E E
G G
G
T
T
T
T
T
T
W
WV
C
C
E
D
D
C
FH
LP
E
C
S
S
X
H1
H2
N�. R��������:
B�: D���:
REVIEWED BY:
N. H���
DESIGNED BY:
DRAWN BY:
SCALE:
DATE:
MARCH 3,
2013
PROJECT:
687-001
S����
O� 9 S�����
PATEROS CREEK
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� P����������� E������� ��
��� ������ �� N�������
E���������� S�������, I��.
NOT FOR CONSTRUCTION
REVIEW SET
03/13/13
200 S���� C������ A�����, S���� 010
F��� C������, C������� 80524
E N G I N E E R I N G
� � � � � � ��
PHONE: 970.221.4158 FAX: 970.221.4159
���.�������������������.���
CALL 2 BUSINESS DAYS IN ADVANCE BEFORE YOU
DIG, GRADE, OR EXCAVATE FOR THE MARKING OF
UNDERGROUND MEMBER UTILITIES.
CALL UTILITY NOTIFICATION CENTER OF
COLORADO
K��� ����'������.
C��� ������ ��� ���.
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P���� & R���������
T������ E������� D���
APPROVED:
CHECKED BY:
CHECKED BY:
CHECKED BY:
CHECKED BY:
CHECKED BY:
W���� & W��������� U������
C��� �� F��� C������, C�������
UTILITY PLAN APPROVAL
H1
HISTORIC DRAINAGE PLAN
A. R����
N. W�������
1"=60'
NORTH
( IN FEET )
1 ���� = ��.
60 0 60 F���
60
120 180
FOR DRAINAGE REVIEW ONLY
NOT FOR CONSTRUCTION
LEGEND:
4953
PROPOSED CONTOUR 93
PROPOSED STORM SEWER
PROPOSED SWALE
EXISTING CONTOUR
PROPOSED PROPERTY BOUNDARY CURB & GUTTER
PROPOSED INLET
A
DESIGN POINT
FLOW ARROW
DRAINAGE BASIN LABEL
BASIN
DESIGNATION
BASIN
AREA (AC)
DRAINAGE BASIN BOUNDARY
PROPOSED SWALE SECTION
1 1
B2
1.45 ��
FILL RECOMMENDATION
PORTIONS REMAIN IN THE SFHA
This document provides the Federal Emergency Management Agency's determination regarding a request for a Letter of Map Revision based
on Fill for the property described above. Using the information submitted and the effective National Flood Insurance Program (NFIP) map, we
have determined that the described portion(s) of the property(ies) is/are not located in the SFHA, an area inundated by the flood having a
1-percent chance of being equaled or exceeded in any given year (base flood). This document revises the effective NFIP map to remove the
subject property from the SFHA located on the effective NFIP map; therefore, the Federal mandatory flood insurance requirement does not
apply. However, the lender has the option to continue the flood insurance requirement to protect its financial risk on the loan. A Preferred Risk
Policy (PRP) is available for buildings located outside the SFHA. Information about the PRP and how one can apply is enclosed.
This determination is based on the flood data presently available. The enclosed documents provide additional information regarding this
determination. If you have any questions about this document, please contact the FEMA Map Assistance Center toll free at (877) 336-2627
(877-FEMA MAP) or by letter addressed to the Federal Emergency Management Agency, LOMC Clearinghouse, 7390 Coca Cola Drive, Ste 204,
Hanover, MD 21076.
Luis Rodriguez, P.E., Chief
Engineering Management Branch
Federal Insurance and Mitigation Administration
C:\NE\687-001-Pateros Creek\Drainage\Detention\DetentionVolume_FAA Method
3/12/2013
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
11No0.17 0.17 0.21 70 2.00% 11.6 11.6 11.0 0 0.00% N/A N/A 0 N/A N/A N/A 12 12 11
22No0.45 0.45 0.56 45 2.00% 6.5 6.5 5.3 979 0.50% 1.41 11.5 0 N/A N/A N/A 18 18 17
33No0.59 0.59 0.74 43 2.00% 5.0 5.0 3.5 804 0.50% 1.41 9.5 0 N/A N/A N/A 14 14 13
44No0.30 0.30 0.38 170 2.00% 15.4 15.4 14.0 0 0.00% N/A N/A 317 1.00% 1.50 3.5 19 19 17
55No0.62 0.62 0.77 47 2.00% 4.9 4.9 3.4 709 0.50% 1.41 8.4 0 N/A N/A N/A 13 13 12
66No0.33 0.33 0.41 125 2.00% 12.8 12.8 11.4 816 0.50% 1.41 9.6 0 N/A N/A N/A 22 22 21
77No0.13 0.13 0.16 98 2.00% 14.3 14.3 13.8 85 0.50% 1.41 1.0 0 N/A N/A N/A 15 15 15
DEVELOPED TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow
ATC
March 12, 2013
Time of Concentration
(Equation RO-4)
3
1
1 . 87 1 . 1 *
S
Ti C Cf L
10-year Cf = 1.00
March 12, 2013
(min)
10-yr
Tc
(min)
100-yr
Tc
(min)
11No0.17 0.17 0.21 483 1.70% 32.0 32.0 30.5 0 0.00% N/A N/A 0 N/A N/A N/A 32 32 30
22Yes0.09 0.09 0.11 500 1.10% 41.1 41.1 40.2 0 0.00% N/A N/A 425 1.30% 1.71 4.1 45 45 44
HISTORIC TIME OF CONCENTRATION COMPUTATIONS
Gutter Flow Swale Flow
Design
Point
Basin
Overland Flow
ATC
March 12, 2013
Time of Concentration
(Equation RO-4)
3
1
1 . 87 1 . 1 *
S
Ti C Cf L